This invention relates to a printer of dot matrix impact type, and more particularly to an improved printer which changes a relative position between a platen and a printing head for realizing desired printings.
Known is a printer which guides a paper sheet between a printing head and a platen provided with sintered bodies made of nylon impregnated with inks. This kind of the printer is difficult to manufacture because requirements on precision of the platen having a long printing part.
Known is also a printer of this type for printing on a paper of large width, which does not use a platen having a large printing part extending over the full width of the paper, but uses a platen of comparatively short length to be synchronized with a printing head and moved at equal speed therewith.
The printer of this type which moves the platen and the printing head at the equal speed, especially the printer having the printing head of a wire dot matrix impact type, encounters the following problems.
When the sintered bodies of the platen are impacted by means of wires striking against the printing paper sheet, the surface of the sintered bodies becomes deformed and depressed. The depression caused by one impact is recovered, but if the same surface is repeatedly impacted, the depression will not recover and the sintered bodies develop non-uniformity on the surface. If the printing is continued, the corresponding part of the paper would be excessively depressed and holes would result. The depressed part caused by the successive imparts delays supplying the ink, or makes the printing ink light.